The current implementation of conversion of clojure.lang.Ratio class to BigDecimal (via bigdec) or to a fixed precision floating point value is not what one would expect. For example:
user> (double (/ (expt 2 1024) 3)) Infinity when in fact it should return: 5.992310449541053E307 and user=> (bigdec (/ 1 2)) 0M when in fact it should return: 0.5M These two issues are the symptoms of two different problems, the first is the current implementation of Ratio.doubleValue which simply converts the numerator and denominator of the Ratio to a double and then divides. The problem with this is that Ratio stores the numerator and denominator as BigInteger objects, and when either of these is greater than the size a double can store it will return +/- Infinity or NaN. This is easily fixed by having Ratio use BigDecimal to do the division at a fixed precision of 64-bits. The second problem is a cause of the definition of the clojure.core.bignum function which has no cond clause for a ratio. This can be solved by adding a clause and having Ratio expose a "decimalValue" function which would perform a BigDecimal division call. There is, however, a catch to this method. If you were to naively implement this you would have (bigdec (/ 1 3)) throw ArithmeticException due to a non-terminating decimal expansion, which would counter to what it currently does, which is always give back a valid BigInteger object or fail at the cast. This could be solved by adding a decimalValueSafe function that would simply catch this and try again at a fixed precision (say double-double 128-bit). The other option would be to force an integer division on these non-terminating expansions, but I think that would be counter intuitive. I have uploaded a diff [1] that has the fairly easy changes that would need to be made to Ratio and bigdec. [1] http://clojure.googlegroups.com/web/ratio-conv.diff?gsc=A8P14BYAAACy2j9kAs1fxLcj8emwRH3H-vghgYgES8zAzJdW7J9-8w --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
